DISEASE

When a person has a disease, a part of that person’s
body fails to function properly. Diseases produce different patterns of
symptoms: knowing these helps a doctor to recognize many different diseases.
Three of the most common categories of disease are HEART DISEASE, INFECTIOUS DISEASES, and CANCER.
Various factors can affect the risk of a disease developing; for example,
smoking is known to increase the risk of many diseases, whereas regular
exercise may reduce the risk.

Table 26. SOME OTHER CATEGORIES OF DISEASE

CATEGORY

CAUSE AND EXAMPLES

Nutritional deficiencies

Lack of an essential nutrient in the diet Example: scurvy, caused by lack of vitamin C

Genetic disorders

Inheritance of faulty genes Examples: cystic fibrosis, haemophilia

Degenerative diseases

Gradual loss of function in body parts Example: osteoarthritis

Endocrine disorders

Disturbance of the body’s hormonal balance Example: diabetes mellitus

Autoimmune diseases

Immune system attacks the body’s own tissues Example: rheumatoid arthritis

HEART DISEASE

Heart disease is caused by narrowing of the coronary
arteries, the vessels that supply blood to the heart muscle. Some factors that
increase the risk of getting the disease are smoking, being overweight, a diet
rich in animal fats, and a lack of exercise. Heart disease is common in rich
countries. Drugs, and in some cases surgery, are used to treat it.

NARROWED ARTERY

The narrowing of the coronary arteries in heart disease is caused
by fatty deposits, called atheroma, on the walls of the arteries.
Atheroma can also develop in arteries supplying the brain. This can lead to a
stroke, in which the blood supply to an area of brain is cut off.

CHOLESTEROL CARRIER PARTICLE

A high concentration of particles like this in the blood is
thought to increase the risk of atheroma. Called low-density lipoprotein
particles, they are composed of fatty substances and some protein. The level of
these particles in the blood tends to be higher if a person’s diet is
rich in fats of animal origin.

INFECTIOUS DISEASES

Infectious diseases are caused by organisms that invade
body tissues or organs and affect their functioning. Infections can be passed
between people and can affect any part of the body. The two main types of
infectious organisms are bacteria and viruses. Other types include fungi,
protozoa, and worms. Some infectious diseases can be treated with
drugs.

BACTERIA

Bacteria are simple, single-celled organisms. Some cause problems
by releasing damaging substances called toxins. The bacteria seen here cause
meningitis, a dangerous inflammation of the coverings of the brain and spinal
cord. Other bacterial diseases include cholera, typhoid, bacterial pneumonia,
and tuberculosis.

HUMAN IMMUNODEFICIENCY VIRUS

Viruses are the smallest infectious particles. They need to invade
other living cells to replicate. The human immunodeficiency virus (HIV) infects
certain white blood cells. Eventually, an infected person is likely to develop
AIDS, a disease in which the body’s immune system is severely weakened.
Viral diseases include colds, flu, measles, and mumps.

CANCER

In cancer, there is rapid and uncontrolled growth of body
cells. These cells are often grouped together as a lump, called a tumour.
Common sites include the lungs, large intestine, and breasts. The tumour may
spread to surrounding tissues and later to other parts of the body. In some
cases, cancer is fatal. However, the various treatment choices mean that it can
often be cured.